The purpose of this study was to investigate the mediating effect of student achievement in mathematics and science in individuals' intergenerational social mobility between parental socioeconomic status (SES) and their future occupational prestige. We also examined the mediating effect of other factors, such as parental expectation for educational attainment. The Longitudinal Study of American Youth (LSAY) 1987-1994 and 2007-2011 data (a sample of 5,945 high school students) were analyzed with structural equation modeling. Our results indicated that high school student achievement in mathematics and science significantly mediated students' intergenerational social mobility between parental SES and their future occupational prestige. Also, achievement in mathematics and science had a lesser effect than students' expectations for future education.